Wells and water.

A house on a well uses water. A horse property on a well uses water on a schedule that does not flex — animals drink daily whatever the aquifer is doing, and an arena needs watering in exactly the weather when everyone else is pumping too.

So the useful questions are these four, in this order:

1. What right does this parcel have to the water?
2. What does the well actually yield, measured rather than remembered?
3. What is in the water, tested by an accredited lab?
4. Who can limit it later, and under what authority?

1. The right, which is not the same as the well

California treats water under your land in two very different ways depending on how it moves. Water in a subterranean stream flowing through a known and definite channel requires a state permit. Percolating groundwater does not — Water Code § 1200 limits the State Water Board's appropriation authority to surface water and those subterranean streams. Most groundwater under most Southern California horse property is percolating, and you take it by using it beneficially.

If you use it on the land above the basin you have an overlying right. Use it somewhere else and it is an appropriative right, which ranks lower. Overlying rights are correlative — a rule from Katz v. Walkinshaw (1903) — meaning every overlying owner shares in proportion during shortage rather than the earliest user taking it all.

Adjudicated basins work completely differently. A court has already determined everyone's rights, appointed a watermaster, and set a safe yield. That guarantees you a proportionate share — and it also means a parcel that is not a party to the judgment may have no right to pump at all, however good the well is. Tehachapi is the clearest local example: three adjudicated basins, one watermaster, and a written acknowledgement for non-party parcels that they have no right to the native yield.

How that plays out in Tehachapi →

Judgments are recorded, which means they are constructive notice to every buyer. “Nobody told me” is not a position available later.

2. Yield, and the report that is already public

Most buyers do not know this: Well Completion Reports have been available on request since June 24, 2015, under Water Code § 13752(a). The Department of Water Resources holds them and publishes a map application. The report tells you when the well was drilled, how deep, how it was constructed and sealed, and what the driller measured at the time.

One trap, and it is a big one on acreage: most reports on the public map are geolocated to the centre of a one-square-mile section, not to the wellhead. A dot near the property is not evidence of a well on the property. Use the report for its contents, not its position.

A driller's figure from 1978 is also not today's yield. Have the well tested, under load, by a licensed contractor — C-57 for the well itself, C-61/D-21 for the pump.

On what counts as an adequate yield, be careful with numbers you are given. California has no statewide minimum. Riverside County applies a standard of 1 gallon per minute sustained over four hours for a domestic well. That is a county standard, not a state one, and Orange and Los Angeles counties do not publish an equivalent figure we could verify. Anyone quoting you a universal GPM minimum is repeating something they have not checked.

One gallon per minute is 1,440 gallons a day if it never stops. Set that against the horse figures further down before you assume it is comfortable.

3. What is in it

Test through a laboratory accredited under California's ELAP programme. Two things are routinely reported wrong:

• The arsenic limit is 0.010 mg/L, and has been since November 28, 2008. You will still see 0.05 quoted — that is the pre-2008 figure and it is five times too permissive. Arsenic is naturally occurring in parts of Southern California groundwater.
• Total coliform has no numeric limit. Under the Revised Total Coliform Rule it is handled as a treatment technique, not a maximum contaminant level. E. coli is the one carrying a numeric standard. “Zero coliform allowed” misstates how the rule works.

On a horse property also ask about nitrate, which is the contaminant most plausibly connected to animal keeping and septic on the same parcel.

4. Who can limit it later

This is the part most likely to be misunderstood, and the misunderstanding always runs in the reassuring direction.

“Domestic wells are exempt from SGMA” is not true as stated. Under the Sustainable Groundwater Management Act, de minimis extractors are exempt from metering and reporting and conditionally from fees. But Water Code § 10726.4 allows a groundwater sustainability agency to regulate, limit or suspend extraction from individual wells, and that section carries no de minimis carve-out.

So the accurate version is: your domestic well is probably exempt from the paperwork. It is not categorically exempt from the agency's authority. Which agency covers the parcel, and what its plan says, is a question worth asking before you buy rather than after a drought.

A related correction: you will see 2040 and 2042 quoted as SGMA deadlines. The statute sets 20 years from plan implementation, with up to two five-year extensions available — so those dates are shorthand, not fixed law.

Setbacks: never accept a single number

How far a well must sit from a septic tank, a leach field, a seepage pit or an animal enclosure differs by county. Orange, Riverside and Los Angeles counties each publish their own, and they do not agree. Riverside additionally imposes a property-line setback that the others do not.

This page deliberately does not print a table, because a single figure presented as universal is the most common error in this subject and the one most likely to cause an expensive mistake on a specific parcel. Call the county with jurisdiction:

• Orange County Environmental Health — (714) 433-6287
• Riverside County Environmental Health — (951) 955-8980
• Los Angeles County Public Health, Drinking Water Program — (626) 430-5420

In Los Angeles County a new domestic well cannot be used until it meets state drinking water standards, at which point the county issues a Water Supply Approval Letter. That is a transaction-relevant document and worth requesting.

Standards note: DWR Bulletin 74, the underlying well standards document, is being rewritten. Anything in this area should be re-confirmed rather than assumed stable.

The disclosure gap nobody mentions

California's Transfer Disclosure Statement includes a “Water Supply” item where a seller identifies City, Well, Private Utility or Other. So the existence of a well is disclosed.

Beyond that, there is no statutory well protection for a buyer. We could find no California statute requiring a standalone well disclosure form, a yield test, or a water quality test as a condition of sale. The TDS itself says it is not a warranty and not a substitute for inspections.

Which means well testing is contractual, not statutory. If it is not written into your offer, it does not happen. On a property where the water is the difference between a working horse property and a very expensive field, that is the single most important sentence on this page.

How much water do horses actually use?

Enough that the answer changes which properties work.

University extension sources put a mature horse at maintenance somewhere between 5 and 12 gallons a day — and they genuinely disagree within that band. Penn State says 5 to 10; Minnesota says 8 to 10 for a 1,000-pound horse; other extension sources put the typical range at 10 to 12, or 5 to 15 depending on temperature, humidity and workload. Working horses in summer heat are commonly cited at 12 to 20 gallons a day.

We are giving you the spread rather than a single number because the published sources do not agree on one, and a page that picks a figure and states it flatly is pretending to a precision that does not exist. Plan conservatively. Four horses at the top of the working range is around 80 gallons a day before a single thing has been washed.

On total property demand — wash racks, arena dust control, barn cleaning, irrigation — we found no authoritative figures at all, and will not invent any. Arena watering in particular is highly variable and can dwarf everything else. If you are buying on a well with an arena, that is a question for the seller about their actual usage, and for a well contractor about whether the system can sustain it.

What to do, in order

1. Ask whether the parcel is in an adjudicated basin, and if so whether it is a party to the judgment and what it is allocated.
2. Identify the groundwater sustainability agency, if any, and what its plan contemplates.
3. Pull the Well Completion Report from DWR — and do not treat the map location as the wellhead.
4. Write testing into the offer. Yield under load and water quality through an ELAP lab. Nothing requires it but your contract.
5. Confirm setbacks with the county, especially where a barn, corral or septic system sits near the wellhead.
6. Ask the seller what they actually use in August.